We propose to study experimentally the physical-chemical processes controlling the growth of hygroscopic medicinal aerosols in the human respiratory tract and to use the results to refine and apply existing theoretical aerosol growth models to the respiratory tract. Growth rate measurements will be made on various drug aerosols and surface active additives will be tested. Temperature and relative humidity measurements will be made in the large airways of more human subjects. Other clinical studies will use monodisperse drug aerosols to investigate the site of action of the drug or bronchodilator in asthmatic and normal human subjects. A pressure compensated flow body plethysmograph has been developed to aid in determining the site of airway response. Gamma scintillation cameras may also be used to visualize the tagged drug deposition sites. Spinning top or disc systems will be used to generate the monodisperse drugs. Deposition studies in hollow airway casts will be continued for measurement of total and regional deposition, and the effects of pulsatile versus steady flow will be studied. Mathematical modeling of deposition will concentrate on developing a breathing cycle deposition model which can be used to predict the deposition sites of therapeutic aerosols.